Don't size a hot-water boiler by measuring the radiators
If you have more piping and radiation than you have steam to heat it, the steam won't make it to the end of the run. You'll wind up with a cold house that costs a lot to heat, and inadequately at that, but I think you're making a mistake if you size a replacement hot water boiler that way." He shook his head. "That's the way I do it.